Polysilicon is used as a starting material for semiconductors or wafers in solar applications. The use of such polysilicon must be highly pure (e.g., for semiconductor applications at least 99.9999999% pure (i.e., nine nines pure) and for solar applications at least 99.9% pure. In order to prevent issues with a reduction in desired properties, such as electrical properties, the polysilicon should not be mixed with metal impurities wherever possible.
Polysilicon is typically produced by reducing a silicon compound, such as trichlorosilane, with hydrogen and formed into rods. The polysilicon rods are then crushed or broken into smaller pieces. Contaminant or impurities imparted to the polysilicon pieces during the crushing can be removed by etching after which the polysilicon is passed through water and dried and then conveyed to be sorted for further processing or packaging. During each step, the polysilicon can be contaminated with impurities such as metal or polymeric impurities. Steps must be taken to prevent this contamination that will affect the purity of the polysilicon product.